The invention relates to an electromagnetic brake having brake segments that are elastically disposed at a shaft or a part connected with said shaft, and that interact with an electromagnetic brake stator or brake magnet which forces the brake segments against a stationary braking area or lifts them off said braking area.
In the case of known electromagnetic brakes of this type, a brake disk, as the brake segment, is mounted at the shaft or at a hub part arranged on the shaft by spring elements to move in an axial direction but fixed so as to essentially not be rotated relative to the shaft. The spring elements, that are leaf springs, can be manufactured only with large tolerances. Thus, a relatively extensive adjusting device is necessary in order to ensure a sufficiently reproduceable position of the brake disk when the brake is not actuated. If necessary, the manufacturing tolerances can be reduced if the brake disk are guided axially on the shaft or the hub part by interacting grooves and recesses. However, arrangements of this type tend to generate noise. Under certain circumstances, tolerances that are too low and when the brake is not actuated may cause the brake disks to grind at the brake magnet or at the stationary braking area.
In known electromagnetic drum brakes, the brake shoes are pressed from the inside against the brake drum by an electromagnet that is arranged transversely to the drum brake. For this purpose, the brake shoes, that are curved in axial view of the brake drum at one end, are disposed to be pivotable around an axis parallel to the axis of the drum. The electromagnet is applied to the other end of the brake shoes. Arrangements of this type also require careful adjusting that must be checked from time to time in order to compensate for the wear of the brake shoes. The adjusting is necessary because the adjusting forces generated by the electromagnet also depend on the adjusting path that becomes continuously longer because of the wear of the brake shoes.
It is therefore the objective of the invention to provide an electromagnetic brake that is constructively simple, and provides reproduceable braking forces with minimal adjustments.
This objective is achieved by a brake stator or brake magnet having two ring-shaped pole pieces that are arranged concentrically to the axis of the shaft and can be oppositely magnetized, and brake segments being arranged radially adjacent or concentric to the pole pieces with radial mobility at the shaft or at a hub part or the like and connected with said shaft are acted upon by springs that force the brake segments from the pole pieces and towards stops on the shaft or on the hub part.
Since the brake segments, when the brake is not actuated, take up a fixed, constructively indicated position, any precise adjusting in this case is not required. In addition, the braking force is extensively independent of the wear of the brake segments. The reason is that in the position when the brake is in effect, the brake segments are magnetically attracted by the ring-shaped pole parts and will close the gap between the pole parts irrespective of the wear. The magnetic forces between the brake segments and the pole parts are most extensively independent of the material thickness of the brake segments.
In a preferred embodiment of the invention, the brake stator or brake magnet has an annular coil that is arranged concentrically with respect to the shaft axis in a magnetically soft or hard ring housing having an annulus that is radially open on the side facing the brake segments. This results in an extremely compact and constructively simple brake stator or brake magnet. The ring housing, with respect to an axial plane, has a horse-shoe-shaped or preferably rectangularly U-shaped cross-section that, if necessary, also permits a segmented construction.
This is an advantage particularly when the ring housing is a permanent magnet that tries to pull the brake segment continuously into the position in which the brake is in effect, and the coil is able to generate a magnetic field that is opposite to the field of the permanent magnet in order to release the brake. In this case, a ring-shaped permanent magnet may easily be arranged as part of a softly magnetic ring housing.
If necessary, a friction surface may be arranged between the edges of the front sides of the ring housing or the pole parts on the side of the brake segments that interacts with the brake segments and consists of a non-magnetizable material. However, it is also possible for the pole parts or the front sides of the ring housing to interact directly with the brake segments.
If the brake stator or the brake magnet is to be operated by alternating current, rectifier elements that are connected to the coil may be housed inside the ring housing or in recesses of said ring housing so that again an extremely compact construction is made possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.